This invention pertains to mercury displacement relays, and more particularly to an impulse mercury relay with magnetic interlock switch for use in electrical circuits, especially for circuits requiring interlock relays actuable by an electrical impulse of relatively short duration.
It is well known to those familiar with electrical circuits that often an electrical interlock switch is needed to protect or ensure proper functioning of electrical machines and equipment. For example, with electrically-operated mining machinery, the operator should be prevented from simultaneously switching the machinery into both forward and reverse positions to avoid damaging the machinery. This can be accomplished if a normally-closed switch in the forward gear contactor is wired into the reverse gear contactor. Moreover, if it is desired, a time delay element can be added to the interlock switch to establish a period of time which must elapse before switching or shifting between forward and reverse gear contactors.
Although interlock switches, such as described above, have been satisfactorily used in electro-mechanical devices, they have generally not been satisfactorily designed for use in mercury displacement relays in electrical circuits.
Further, it can be desirable to operate an electrical relay with an impulse, i.e., a coil actuation of short duration, after which the electrical contacts remain closed by a latching mechanism. Generally, this mechanism is mechanically employed in electro-mechanical relays and mercury displacement relays. One of the problems with prior art mechanical latching mechanisms in mercury displacement relays is that some of the mechanical latching elements can be exposed to the intense arcing environment in the electrode above the mercury level, and therefore prematurely fail because of erosion and heat damage caused by the arcing.